The present invention relates to a recording apparatus for recording image data on a printing sheet. More particularly, the present invention relates to a thermal transfer recording apparatus for recording an image on a printing sheet by operating each thermal head in accordance with the depth of image data to be printed while moving the printing sheet with respect to a thermal head having a plurality of heat generating devices.
A thermal transfer recording apparatus is also called as a thermal transfer printer. The thermal transfer recording apparatus is a recording apparatus having a structure such that a thermal head is pressed against an ink ribbon placed on a printing sheet wound around a cylindrical platen and ink is melted or sublimated so as to transfer color pigment to the surface of the printing sheet. The thermal head has a plurality of heat generating devices (heaters) horizontally forming a line, the heat generating devices being arranged to relatively move for a predetermined length while being brought into contact with the printing sheet. Then, the heat generating devices are caused to generate heat for a period corresponding to the depth of each pixel for each line so that one image is printed.
When a color image is formed by a thermal transfer recording apparatus of the above-mentioned type, three color tones, that is, Y (yellow), M (magenta) and C (cyan) images, or four color tones including K (black), are sequentially printed. The color tone to be realized by printing is expressed by adjusting the degree of superposition of yellow, magenta and cyan components.
When the thermal transfer recording apparatus prints yellow components in a yellow-component printing step, the thermal head is operated while rotating the platen to move the printing sheet with respect to the thermal head so that data of the yellow components is printed. In a next magenta-component printing step in which magenta components are printed, the platen is furthermore rotated to restore the printing sheet to the original position so that magenta components are printed similarly to the yellow-component printing process. In a next cyan-component printing step in which cyan components are printed, the platen is furthermore rotated to similarly restore the printing sheet to the original position so that cyan components are printed similarly to the magenta-component printing process. That is, similar printing steps are repeated three times. If an ideal operation is performed, yellow, magenta and cyan dots are printed at appropriate positions so that an appropriate color is reproduced.
However, the structure arranged such that the platen is rotated to physically locate the printing sheet sometimes encounters a fact that the printing sheet cannot completely be restored to the original position when the magenta-component printing step is performed or the cyan-component printing step is performed. In the above-mentioned case, displacement for several microns takes place at the dot position for each color component. Since the yellow, magenta and cyan dots are linearly arranged in a direction in which the heat generating devices are arranged, that is, in the main scanning direction, displacement of the dot position of each color causes linear moire fringes to be generated in the main scanning direction.
Since yellow, magenta and cyan dots are printed in this sequentially order and the half tones are expressed by adjusting the degree of superposition of the yellow, magenta and cyan components, relative displacement taking place between, for example, the yellow dot and the magenta dot results in a dot having a hue different from a required one being unintentionally formed. That is, color balance is disordered and color confusion takes place.
In view of the foregoing, an object of the present invention is to provide a recording method and a recording apparatus capable of preventing generation of moire fringes and color confusion occurring attributable to displacement of recorded dots.